Seals are used between inner and outer wellhead members to contain internal well pressure. The inner wellhead member may be a casing hanger located in a wellhead housing that supports a string of casing extending into the well. Alternatively, the inner wellhead member could be a tubing hanger that supports a string of tubing extending into the well for the flow of production fluid. The tubing hanger lands in an outer wellhead member, which may be a wellhead housing, a Christmas tree, or a tubing head. A packoff or seal, seals between the inner wellhead member and the outer wellhead member. In addition, emergency annulus seals can be used in case the packoff seal fails.
However, sometimes all of these seals fail to maintain pressure integrity and contingency sealing measures must be taken. Bridging hangers are typically used as a contingency sealing option when both primary and emergency annulus seals have failed to maintain pressure integrity. A bridging hanger may replace the faulty seal with two separate seals, one to the hanger below and another to the housing. An elastomeric face seal may be used to form the seal between the bridging hanger and the casing hanger below. The elastomeric seal may degrade, or become damaged, thus compromising the seal that the contingency option needed to provide. This same problem may occur between lockdown hangers sealing to a hanger below and in addition may require the use of a long isolation sleeve extending to the hanger below when such is required.
A need exists for a technique that addresses the failures of contingency seals, increases the robustness of contingency sealing options, and minimizes isolation sleeve length requirements when lockdown hangers are employed. The following techniques may solve one or more of the problems provided above.